1. Field of the Invention
The present invention relates to a light emitting module including a light emitting element, such as a light emitting diode.
2. Description of the Invention
In recent years, LEDs (Light Emitting Diodes) by which power saving can be expected draw attentions as light sources for lighting apparatuses from growing interests in environment. A structure in which an LED chip and a phosphor are combined together is known as a lighting apparatus using an LED, which emits white light.
In such a structure, because the light from the LED chip is emitted in all directions after the wavelength thereof has been converted by the phosphor, part of the light whose wavelength has been converted returns again toward the LED chip to be absorbed there, and disappears after turning into heat. As a result, an efficiency of extracting light from the LED chip is decreased.
Accordingly, a light emitting apparatus including a wavelength-selective filter layer has been devised, in which the wavelength-selective filter layer transmits the light emitted from an LED chip and reflects the visible light emitted from a phosphor (see Japanese Patent Application Publication Nos. 2008-270707 and 2008-235827). Thereby, it is said that absorption of part of the visible light emitted from the phosphor, occurring when the part of the visible light returns to the LED chip, can be suppressed and a decrease in a light extraction efficiency can be prevented.
However, in the light emitting apparatus described in the aforementioned Patent Document 1, there is an air layer between the LED chip and the wavelength-selective filter layer, and the difference between the refractive index of the LED chip and that of air is large, and hence the light in the LED chip is likely to be confined therein. As a result, an amount of the extracted light is small, and hence the light emitting apparatus cannot be one having a high luminance. In addition, in another embodiment in which the LED chip is covered with glass, the surface area of a light emitting layer becomes large, and hence the light emitting apparatus cannot be one having a high luminance. In the light emitting apparatus described in Patent Document 2, a sealing resin is present between the LED chip and the wavelength-selective filter layer, and hence an efficiency of extracting light from the LED chip is improved. On the other hand, in a light emitting apparatus having a sealing resin, an angle (incident angle) at which the light from the LED chip is incident on the wavelength-selective filter layer has a great influence on the transmittance of the wavelength-selective filter layer in comparison with the case where there is no sealing resin. In particular, as the incident angle is larger, the transmittance of light is more decreased. As a result, the light emitting apparatus cannot be one having a high luminance. In addition, in the light emitting apparatus described in Patent Document 2, the thickness of the sealing resin is large, and hence the light from the LED chip spreads before reaching the filter layer and the light is absorbed by the sealing resin, thereby an improvement in the luminance is also hampered.